Trabeculectomy (guarded filtration procedure) with tissue re-enforcement

ABSTRACT

An ocular implant ( 10 ) is disclosed for beneficially inhibiting wound healing, inflammation, and devastating infection following a guarded filtration procedure. The implant ( 10 ) is comprised of a thin implantable material contoured to fit the eye. During a guarded filtration procedure, the implant ( 10 ) is positioned at the edge of the sclerectomy site, under the scleral flap ( 7 ), and extends laterally and posteriorly from the sclerectomy site. The implant ( 10 ) significantly inhibits adhesion and scarring at the surgical site, and eliminates the need for anti-scarring medications, thereby reducing the risk of blinding infections.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to ocular implants, and, morespecifically, to improved methods and devices useful in performing atrabeculectomy or guarded filtration procedure (GFP), that beneficiallyinhibit wound healing, inflammation, infection, and scarring following aguarded filtration procedure.

BACKGROUND OF THE INVENTION

Glaucoma is a progressive eye disease, which affects millions of adultseach year. If left untreated, glaucoma causes partial or totalblindness, and is among the leading causes of blindness in allcountries. Glaucoma occurs when the pressure inside the eye rises abovesafe levels due to poor drainage or blockage of the aqueous (the fluidproduced inside the eye) outflow channel, or due to increases in venouspressure outside of the eye. The increased intraocular pressure damagesthe tissues in the eye, especially the optic nerve, which eventuallycauses blindness.

One method for treating progressing glaucoma is a trabeculectomy (alsoreferred to as guarded filtration procedure (GFP)). In traditionalguarded filtration surgery, the sclera is exposed, and a scleral flap isdissected in the scleral tissue. The scleral flap is elevated and pulledforward to reveal a bed of scleral tissue under the flap. An incision(referred to as a sclerectomy) is made through the scleral bed to createa “window” or fistula into the anterior chamber of the eye, which allowsthe aqueous (the fluid produced in the eye) to flow out of the anteriorchamber, thereby alleviating the intraocular pressure. The scleral flapis sutured over the fistula, creating a small space under the flap whichallows the aqueous to drain from the eye, yet provides enough resistanceso that excess aqueous does not escape, thus reducing the risk ofhypotony.

A major problem with filtration surgery in general is the eye's ownnatural wound healing response, which causes the fistula to close orotherwise heal too rapidly, which, in turn, causes the filtration (i.e.drainage) to fail. Attempts to overcome this problem have includedinserting ophthalmic devices such as tubes, valves, or shunts into thefistula in order to maintain the fistula open. These conventionaldrainage devices have been widely used with varying degrees of success.Examples of such devices are disclosed in U.S. Pat. Nos. 5,178,604;5,397,300; 5,868,697; 5,879,319. However, these implants often becomeclogged, obstructed, or restricted by the proliferation of scar tissueand adherence of the tissue layers, which occur at the surgical site.Most of these implant devices can also cause restriction of eyemovement, incapacitating double vision, and eye discomfort. In addition,to counteract the natural healing process and closing of the fistula infiltration surgery, antimetabolite drugs are commonly used in filtrationsurgery to inhibit the wound healing process. Unfortunately, a majorcomplication of using antimetabolites is that they weaken and thinhealthy tissues, increasing the risk of developing a blinding infectionby nearly ten-fold.

U.S. Pat. Nos. 4,634,418 and 6,102,045 disclose other types of drainagedevices that are constructed of absorptive material that act as wicks orabsorb the aqueous which drains from the anterior chamber of the eye tothe area beneath the scleral flap. However, these devices do not addressthe scarring around the scleral flap, which causes guarded filtrationprocedures to fail.

It is thus one object of the present invention to provide a method andimplant for beneficially inhibiting wound healing in the eye that wouldotherwise cause unwanted closure of the surgical fistula.

It is another object of the present invention to provide an ophthalmicimplant made of an appropriate biocompatible material, and of anappropriate size and shape to effectively inhibit unwanted wound healingin the eye following filtration surgery.

It is yet a further object of the present invention to provide a simplemethod for positioning the implant during a guarded filtrationprocedure.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to trabeculectomy (GFP) with tissuere-enforcement that avoids the need to use antimetabolites or otheragents often employed for improving the success rate of glaucomafiltration surgery, while reducing the rate of devastating infection andother complications. The procedure involves the placement of an implant,which acts as a mechanical barrier between the tissues that tend to scarand adhere to one another at the surgical site. Thus, the implantimproves the long-term success rate of the filtration procedure, anddiminishes post-operative infection rates. The implant is made ofimplantable-grade material of approximately 7 mm×10 mm dimensions, andis contoured to conform to the globe of the eye.

The method of the present invention, in a preferred embodiment, involvesthe steps of exposing the sclera, dissecting a scleral flap, performinga sclerectomy, and then securing a thin, implantable-grade biocompatiblematerial such as silicone, methylmetacrylate, or another material towhich tissues do not adhere (from henceforth to be referred to as the“implant”), to the posterior sclerectomy edge, under the scleral flap.The implant is secured in several places, as needed, and trimmed to fitthe surgical site. The implant extends several millimeters posteriorlyand to the sides of the sclerectomy site. Then, the scleral flap issecured to the implant using, for example, non-absorbable sutures. Thetightness of the sutures is adjusted to prevent overflow and ocularhypotony, but to allow for a reasonable amount of aqueous to escape fromthe anterior chamber of the eye (filtration) in an amount sufficient tocontrol the eye pressure. Finally, the conjunctiva and tenon are closed,and antibiotics and steroids are injected under the conjunctiva.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a through 1 d are top views (surgeon's views) of the major eyecomponents and diagrammatically illustrate the steps associated with thepositioning of the implant during a guarded filtration procedure.

FIG. 2 is a vertical cross-sectional side view of the eye, illustratingan implant made of a silicone sheet material in place following theguarded filtration procedure.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, in accordance with the invention, an implantable-gradesheet material is implanted so that it is positioned centrally, alongthe posterior edge of the sclerectomy site, and extends laterally onboth sides over the sclera. The geometry of the implant is fashioned toallow it to conform to the globe of the eye, and to remain affixed tothe tissue of the eye (sclera).

One preferred embodiment of the implant, and a method for positioning iton the eye, is illustrated in FIGS. 1 a through 1 d. The implant 10 isbest seen in FIG. 1 b, which illustrates an implant after it has beentrimmed by the surgeon to fit the surgical site. In this embodiment, theimplant has a rectangular base, preferably about 5 mm×10 mm in size, andan anterior extension of approximately 3 mm×5 mm. Of course, the actualdimensions and geometry of the implant sheet 10 will depend on thespecific patient including, but not limited to, such factors as thesurgical site condition, the amount of scar-free tissues available, andthe severity of the glaucoma. The latter is a factor because the size ofthe implant will determine the size of the aqueous bleb (which containsthe aqueous outflow) formed under the conjunctiva and Tenon's capsule(the outermost layers of the eye), thus determining the amount offiltration and the resulting intra-ocular pressure. Therefore, theimplant could be trimmed by the surgeon into almost any shape that wouldachieve the desired effect.

The thickness of the implant is less than 100μ, preferably 25-50μ. Theimplant should thus be thin enough not to cause an elevated mass underthe conjunctiva and Tenon's capsule, but still strong enough towithstand suturing through it without tearing. The “implantable-grade”(i.e. safe and tolerable to the eye tissues) material, such as silicone,for example, is highly flexible due to its thinness, yet equally strong.In a preferred embodiment, the implant is manufactured pre-molded toconform to the average eye globe. For example, the average eye has adiameter of 22 to 24 mm, therefore the radius of curvature of theimplant is preferably about 11-14 mm. Other radii of curvature can bemanufactured to fit different globes.

Silicone or methylmetacrylate are preferred as possible implantmaterials because they have been in long-term, widespread use asmaterials for various types of implants in and around the eye. Forexample, silicone and acrylic intraocular lens implants to replace theremoved cataractous lenses in modern cataract surgery have been in usefor many years with excellent safety and tolerability records.Similarly, silicone has been widely used over the years in tube shuntsand valves for glaucoma surgery, in periocular bands for retinaldetachment surgery, and in orbital fracture bone replacements. However,this invention also contemplates the use of any other biocompatiblematerials to which tissues do not adhere, and which are equally safe andtolerable for use in the invention. Many of such related materials arealso demonstrating excellent safety records as intraocular andperiocular implants.

As mentioned above, FIGS. 1 a through 1 d depict a preferred embodimentof the implant and procedure. In FIG. 1 a, following local anesthesia,the Tenon's capsule and conjunctiva 4, covering the sclera 6, are cutfrom the limbus 3 and retracted backward, to create a fornix-based flap5 (the fornix forms the cul-de-sac of the conjunctiva, under the lid;the limbus forms the border between the cornea and where the white ofthe eye begins). GFP can also be performed using a limbus-based flap,where Tenon's capsule and conjunctiva are severed at the upper fornixand dissected and retracted forward until the limbus is reached. Thefornix-based Tenon's capsule and conjunctiva flap cannot be seen inFIGS. 1 a through 1 c, as it is pulled back toward the reader, thereforeonly the space under the flap, whose border is depicted at 5, revealingthe exposed sclera 6, is drawn in FIGS. 1 a through 1 c for simplicity.

A partial-thickness limbus-based scleral flap 7 (partial thicknessrefers to a flap that is dissected, for example, two thirds of the wayinto the sclera, therefore one third of the sclera remains in the flapbed 8) is dissected in the exposed sclera 6 at the limbus 3. The scleralflap is then elevated and pulled forward toward the cornea 1 to exposethe scleral bed 8. A sclerectomy (trabeculectomy) is then performedwhere part of the eye wall is removed in the scleral bed 8, resulting ina “window” or fistula 9 into the anterior chamber of the eye 2. At thispoint, the aqueous can drain from the anterior chamber of the eyethrough the sclerectomy, thus lowering the eye pressure.

Referring to FIG. 1 b, a thin sheet of an implantable-grade implant 10,preferably, between 25 and 50 μm, is secured at the locations indicatedby “X”, centrally at the posterior edge of the scierectomy site, so asnot to obstruct the fistula, and lateral to the scleral bed on bothsides. As stated earlier, the implant's final size is dependent uponsuch factors including, but not limited to, the size of the eye, thesurgical site conditions, and the amount of scar-free and healthytissues available. Additionally, the implant has a radius of curvatureconforming to the contours of the eye globe. At this stage, the aqueouscan still drain from the anterior chamber without resistance.

As shown in FIG. 1 c, next the scleral flap is laid down as depicted at11 to cover the fistula and part of the implant. The scleral flap issecured loosely enough to allow reasonable flow of aqueous from theanterior chamber through the sclerectomy, allowing the relief ofexcessive intra-ocular pressure. The sutures are nevertheless tightenough to prevent hypotony. The manner of securing the implant, alongwith the number of sutures used, depends on the degree of filtration andintra-ocular pressure desired. In addition, the posterior and lateralportions of the implant are tucked under the conjunctiva and Tenon'scapsule layers, as shown by the dashed lines at 12. Usually, noadditional sutures are necessary to secure the implant in those areas.After this point, the implant will prevent scarring and adherence of thescleral flap to the scleral bed, posterior and posterolateral to thesclerectomy site, and will prevent scarring and adherence between theTenon's capsule and the episclera, the most common cause of failure offiltration with time. As a consequence, filtration will be maintainedwithout the use of complication-causing, anti-scarring antimetabolitessuch as mitomycin C and 5FU, which are currently in use to preventscarring.

Finally, as shown in FIG. 1 d, the Tenon's capsule and conjunctiva arelaid back down so as to completely cover the surgical site, and suturedback to the limbal cornea as shown at 13. The hatched Xs are the coveredsutures of the scleral flap and implant which were shown in FIG. 1 c.The final sutures are done so that fluid is unable to escape to the“outside world”, thus, rendering the surgical site “water-tight, andrestoring the external anatomy of the eye.

FIG. 2 is a vertical, cross-sectional view of the anterior eye, throughthe surgical site, illustrating the implant in one preferred embodimentas a silicone sheet under the conjunctiva and Tenon's capsule layers,inside the sclera and scleral flap. The scierectomy, as shown, allowsthe aqueous from the anterior chamber to drain under the scleral flap tothe space under the Tenon's capsule and conjunctiva layers, which thenforms a fluid-filled “bleb” containing the excess aqueous. The implantprevents the tissues from adhering to one another. Optionally, aniridectomy can be done to prevent the iris from adhering to thesclerectomy and obstructing drainage.

EXAMPLE Animal Studies

In a recent rabbit study of the GFP (trabeculectomy), GFPs wereperformed in 14 nonglaucomatous eyes of 7 albino rabbits. In all 7, theright (study) eye underwent a GFP with a 100μ thick, implantable-gradeimplant made of a silicone sheet that extended from the posteriorsclerectomy edge under the scleral flap, to several millimetersposterior and lateral to the scleral flap, under the conjunctiva andTenon's capsule. GFPs were performed without a silicone implant in all 7left (control) eyes. During the post-operative follow-up, conjunctivalhyperemia and chemosis, anterior chamber reaction and lacrimation weregraded. At the end of the follow-up period, 14-91 days followingsurgery, intra-ocular pressure (IOP) was measured with a Tonopen and therabbits were sacrificed.

All 7 (100%) study eyes (GFP, with silicone implant) demonstrated a blebat the end of the follow-up period, compared to only 1 of 7 (14.3%)control (GFP alone) eyes (p=0.001). IOP was lower in the study eyescompared to control eyes (8.3±1.8 mmHg vs. 10.6±1.3 mmHg, p+0.047).Hyperemia and chemosis scores were lower in the study eyes compared tocontrol eyes (hyperemia: 0.94±0.74 vs. 1.33±0.86, p=0.001; Chemosis:0.561±0.50 vs. 0.77±0.57, p=0.004). Anterior chamber reaction andlacrimation scores were similar in study and control eyes. Thus, implantimplantation increases GFP success rate in albino rabbits.

Although the invention has been described with reference to specificembodiments, the description is intended to be illustrative of theinvention and is not intended to be limiting. Various modifications andapplications may occur to those skilled in the art without departingfrom the true spirit and scope of the invention as defined in theappended claims.

1. An ocular implant comprising implantable-grade material that inhibitsadhesion and scarring of eye tissue following a guarded filtrationprocedure.
 2. The ocular implant according to claim 1 wherein theimplantable-grade material is silicone.
 3. The ocular implant accordingto claim 1 wherein the implantable-grade material is methylmetacrylate.4. The ocular implant according to claim 1 wherein the implantable-gradematerial is any biocompatible material to which tissues do not adhere.5. A kit comprising the ocular implant according to claim
 1. 6. A methodfor inhibiting adhesion and scarring following a guarded filtrationprocedure comprising positioning an ocular implant made ofimplantable-grade material at the edge of the sclerectomy site, underand around the scleral flap, such that said implant extends laterallyand posteriorly from the sclerectomy site.
 7. The method according toclaim 6 wherein the implantable-grade material is silicone.
 8. Themethod according to claim 6 wherein the implantable-grade material ismethylmetacrylate.
 9. The method according to claim 6 wherein theimplantable-grade material is any biocompatible material to whichtissues do not adhere.